Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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potassium bromide : KBr
sodium nitrite : NaNO2
sulphuric acid : H2SO4
Class:
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elem=N,Br
redox
Summary:
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Nitrite gives rise to formation of a blue compound with dilute sulphuric
acid, which is not very stable (dissociates into nitrous oxide easily).
When bromide is added, then a brown/green compound is formed, which
is not bromine.
Description:
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Sequence 1:
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Prepare a concentrated solution of sodium nitrite and add some dilute
sulphuric acid (appr. 1 mol/l): The liquid becomes light blue and a gas is
evolved. The gas mixture above the liquid becomes pale brown. When the
liquid is shaken, then it starts bubbling again and a colorless gas is
produced in that case.
Keep container capped and shake a few times: The brown color in the gas
mixture above the liquid disappears again. The final result is a colorless
gas mixture above a very light blue liquid.
Allow some air to mix with the colorless gas mixture above the liquid: The
gas mixture becomes brown again. This reaction occurs almost instanteneously.
Sequence 2:
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Prepare a concentrated solution of sodium nitrite and potassium bromide and
mix these solutions: No visible reaction, the liquid remains colorless.
Add some dilute sulphuric acid (appr. 1 mol/l): The liquid becomes brown/
green and a gas is evolved. The gas mixture above the liquid becomes brown.
Remove the liquid and add some water and shake well: The gas mixture becomes
colorless again. The brown compound was not bromine, but NO2. If it were
bromine, then the liquid would have been yellow.
Allow some air to mix with the colorless gas mixture above the liquid: The
gas mixture becomes brown again. This reaction occurs almost instanteneously.